Possible to port config over FortiManager?

You can always apply a policy package to another FortiGate but that doesn't affect device-level settings.

You could save a config revision from 1 FortiGate (from revision history) & then import it as a new revision in another FortiGate's revision history (provide the Import option is enabled under Admin Settings).  This should only be done if the firmware version is identical between old & new FortiGates.  And if the model changes, some offline modification of the configuration revision might be required prior to import.